TA m? 



.Fl 



% 



DEPARTMENT OP COMMERCE 



Technologic Papers 



OF THE 



Bureau of Standards 

S* W. STRATTON. Director 



No. 205 

TENSILE PROPERTIES OF 

SOME STRUCTURAL ALLOY STEELS AT 

HIGH TEMPERATURES 



BY 



H. J. FRENCH, Physicist 
Bureau of Standards 



DECEMBER 21, 1921 



T.'Z'-'Z'io^l 6 




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DOCUMENTS ^ V.olON 



2^'a(, oy? 






TENSILE PROPERTIES OF SOME STRUCTURAL 
ALLOY STEELS AT HIGH TEMPERATURES 

By H. J. French 



ABSTRACT 

The report gives results of determination of tensile strength, proportional limit, 
elongation, reduction of area, and strength at fracture throughout the range 20 to 
550° C for four steels containing about 0.38 per cent carbon, as follows: (a) Plain carbon 
steel; (b) 3^ per cent nickel steel; (c) 3 per cent nickel, i percent chromium steel; 
(d) I per cent chromium, 0.20 per cent vanadium steel. 

Brief reference is made to the type of fractures obtained in testing steels at various 
temperatures, and particular attention is paid to comparison of the tensile properties 
of these alloys at 550° C. 

CONTENTS 

Page 

I. Introduction 77 

II. Previous investigations yg 

III. Materials and methods used 81 

IV. Experimental results 81 

1. Tensile tests 81 

(o) Tensile strength 81 

(b) Proportional limit 88 

(c) Elongation and reduction of area 89 

(d) Breaking strength 90 

2. Microscopic examination of fractures go 

V. Summary 91 

I. INTRODUCTION 

In the attempted production of ammonia in the United States 
by the Haber process ^ gradual elongation and ultimate fracture 
of bolts in converter chamber heads have introduced serious oper- 
ating difficulties. Under a mean temperature of 550° C to which 
heads, nuts, and bolts were subjected the elongation of the latter 
was such as to require tightening of the nuts almost daily. The 
use of some of the more commonly employed structural alloy steels 
did not remove this difficulty, and a search of the literatture revealed 
little exact information on which a comparison of the high tempera- 
ture tensile properties of various alloy steels could be based. 

In view of the fact that an investigation of the resistance to 
corrosion by ammonia of various ferrous and nonferrous alloys 

' R. S. Tour, "The direct synthetic ammonia process," Joum. Ind. and Eng. Chem., 12, No. 9, p. 844; 
September, 1920. 

77 



78 Technologic Papers of the Bureau of Standards ivoi.i6 

was in progress in connection with redesign of operating equip- 
ment by the Ordnance Department, the Bureau of Standards 
was requested to undertake determination of the tensile proper- 
ties of a number of structural alloy steels throughout the tempera- 
ture range 20 to 550° C (70 to 1 020° F) . From the combined results 
of investigation of resistance to corrosion of various metals and 
the tensile properties of steels at high temperatiures it was hoped 
that selection of a suitable alloy for withstanding required stresses 
could be made, and if this proved unsatisfactory as regards re- 
sistance to attack by the gases encountered at least a more suitable 
metal lining for the converters could be installed. 

The original plan of procedure included tests of a plain carbon 
steel and a number of structural alloy steels, most of which were 
of acknowledged industrial importance. However, because of the 
desire to keep variations in carbon content at a minimum, diffi- 
culty was encounterfed in obtaining some of the alloys, notably 
carbon-manganese and chromium-molybdenum steels, of the exact 
composition desired, so that this report comprises only tests of 
four steels. 

It is further restricted to tests of these alloys in a normalized 
condition, as data so obtained form a basis of comparison with 
tests of samples first subjected to quenching and tempering. The 
high operating temperatures attained, which reach about 650° C 
(1200*' F), limit the tempering subsequent to hardening to rela- 
tively high temperatures, while the large dimensions of the con- 
verter heads and some of the other parts of the equipment sub- 
jected to high temperatiures, which would introduce difficulties in 
quenching, make the use of a forged or normalized steel highly 
desirable. 

Shortly after completion of the tests about to be described ten- 
sile properties at high temperatures of a number of carbon and 
alloy steels subjected to varying thermal treatments were re- 
ported by MacPherran,^ and in discussion of this paper by Spooner 
considerable additional data were presented. However, the work 
of MacPherran and Spooner was confined, in so far as the elastic 
properties are concerned, to determination of yield point; whereas 
the tests carried out by the present author include determinations 
of the limit of proportionality and strength at fracture, and the 
interpretation of these data is somewhat different from that given 
by either of the authors mentioned. 

^ R. S. MacPherran, "Comparative tests of steels at high temperatures," Proc. Amer. Soc. for Testing 
Materials; 1931. 



French] Alloj/ Stecls at High Temperatures 79 

II. PREVIOUS INVESTIGATIONS 

As already indicated, there was vintil quite recently a scarcity 
of accurate data on the high temperature tensile properties of 
various structural alloy steels. This is still the case as regards 
the effect of temperature on the limit of proportionality, of im- 
portance in design of engineering equipment, and in addition 
there is some disagreement betv^een results reported by different 
investigators for similar alloys. Bregowsky and Spring^ deter- 
mined yield point, tensile strength, elongation, and reduction of 
area from 20 to 550° C (70 to 1020° F) for rolled 30 per cent 
nickel steel. 

In 1 913 Schulz* reviewed available data relating to the high 
temperature properties of turbine materials, but the information 
presented for alloy steels was, in large part, for those containing 
varying proportions of nickel. 

Guillet^ reported, among several special alloys for use at high 
temperattues, a steel containing nickel, chromium, and tungsten 
which showed exceptionally high strength at 750 to 800° C 
(1380 to 1470° F). 

A comprehensive analysis of the effects of high temperatures 
on hardness, tensile and impact properties, freedom from warp- 
age, etc., of steels containing 3 per cent nickel and various 
proportions of chromium, high-speed steels and various chromium 
and chromium-cobalt steels was recently prepared by Gabriel.* 
As regards high tensile strength at elevated temperatures, these 
steels were considered of value in the following order: (i) High 
tungsten; (2) high chromium, high carbon; (3) high chromiiun, 
low carbon; (4) 3 per cent nickel and nickel-chromium. 

In the selection of steels for valves the author recommended 
the different type alloys, as follows: (i) A tungsten steel, (2) a 
steel high in chromium, (3) a nickel steel. 

MacPheixan^ recently reported tensile tests from 20 to about 
650° C (70 to 1200° F) for a variety of alloy steels under different 
heat treatments, as shown in Table i . In discussion of this paper 
A. P. Spooner presented a large number of tests at temperatures 
up to about 870° C (1600° F) for the different steels Hsted in 

' I. M. Bregowsky and L. W. Spring, "The effect of high temperature on the physical properties of some 
alloys." Proc. Int. Assoc, for Testing Materials, VI Congress, VIIi; 1912. 

< Schulz, " Neuere versuche und erfahrungen mit turbinenschauf elm a terial fur hohe temperaturen," Die 
Tiu-binc, 9, p. 243; 1913. 

* L. Guillet, "Alloys having remarkable properties at very high or very low temperatures," Rev. Met. 
11, p. 969; 1914. 

' G. Gabriel, "Comparative values of motor valve steels," Iron Age, 106, p. 1465; 1920. 

' See note 2. 



8o 



Technologic Papers of the Bureau of Standards Woi. id 



Table 2 and, in general, confirmed the work of MacPherran 
where direct comparisons were possible. 

TABLE 1.— Alloy Steels Tested at High Temperatures o. 





Type composition ( 


per cent) 


Condition in which steel was tested 


c 


Mn 


Ni 


Cr 


V 




0.21 




3.25 
33.9 

2.38 
20.78 






Annealed at 802° C (1475° F) 


.25 








Do. 


.34 




0.38 

7.42 

.83 

3.36 




816° C (1500° F) water, 705° C (1300° F) 


.53 






As rolled 


.30 




0.17 


857° C (1575° F) water, 732° C (1350° F) 


.69 






843° C (1550° F) water, 705° C (1300° F) 
Annealed at 802° C (1475° F) 


.72 


0.92 






.82 




.91 


.18 


816° C (1500° F) water, 705° C (1500° F) 











o MacPherran, Amer. Soc. for Testing Materials; 1921. 
TABLE 2.— Alloy Steels Tested at High Temperattires a 



Type composition (per cent) 


Condition in which steel was tested 


C 


Ni 


Cr 


V 


Mo 


W 


0.10 












Normalized 870° C (1600° F) 


.45 












Do. 


.33 


3.5 
2.0 










Do. 


.38 


1.0 
1.0 
1.0 
.50 
1.3 

14.0 
3.2 

31.0 








Do. 


.37 


0.20 






Do. 


.47 




0.35 




Do. 


1.10 




.20 
.20 




Annealed 740° C (1360° F) 
Annealed 730° C (1350° F) 


.48 








.25 








Annealed 790° C (1450° F) 
Annealed 905° C (1660° F) 
Annealed 760° C (1400° F) 


.66 




.70 




15.9 


.20 

















o A. P. Spooner, Proc. Amer. Soc. for Testing Materials; 1921. 

These data, while the most recently presented, are together the 
most comprehensive compilation of tests so far recorded for the 
modem types of structural alloy steels, but consist of determinations 
of tensile strength, elongation, reduction of area, and, in part of the 
temperature ranges given, values for yield point. 



French) 



A Hoy Steels at High Temperatures 



8i 



III. MATERIALS AND METHODS USED 

The four steels tested were made by the electric ftimace process at 
the plant of the Halcomb Steel Co., Syracuse, N. Y., and supphed 
through the Nitrate Division, Ordnance Department, in the form 
of I by >^ inch hot-rolled bars of the compositions shown in Table 
3. After cutting into desired lengths for test specimens the bars 
were normahzed by heating to 800 or 850° C (Table 3) and cooled 
in still air. They were then machined to the form and dimen- 
sions shown in Fig. i . All tests were made with the special ap- 
paratus devised by the author and in the manner previously 
described* in detail. 




Fig. I. — Form and dimensions of test specimen used 
TABLE 3.— Composition and Heat Treatment of Steels Tested 





Composition (per cent) 


Heat treatment: 
Heated for 30 


Steel 


C 


Mn 


P 


S 


SI 


Ni 


Cr 


V 


minutes at tem- 
eiature desig- 
nated and cooled 
in still air 


A 


0.38 
.37 
.39 
.37 


0.56 
.67 
.59 

.74 


0.014 
.021 
.019 
.020 


0.013 
.010 
.009 
.023 


0.14 
.20 
.23 
.21 








850° C 


B 


3.43 
3.05 






800° C 


C 


0.93 
1.04 




850° C 


D 


0.17 


850° C 









IV. EXPERIMENTAL RESULTS 
1. TENSILE TESTS 

(a) TENSII.E Strength. — ^The results of tensile tests at various 
temperattires throughout the range 20 to 550° C (70 to 1020° F) are 
given in Tables 4, 5, 6, and 7, and represented graphically in Figs. 2 
to 5, inclusive. 

' Forthcoming Bureau Tech. Pai>er: Effect of Temperature Deformation and Rate of lyoading on the 
Tensile Properties of Low Carbon Steel Below the Thermal Critical Range. Also H. J. French, "Tensile 
properties of boiler plate at elevated temperatures," Min. and Met., 158, sec. is; 1920. 



too 




Fig. 2. — Tensile properties at elevated temperatures of 0.38 per cent carbon steel 



I 
I 

5 
.1 



m 



ao 



60 



'H) 



20 




300 'fOO 

J 1 1 1 L_ I ■ 

g 100 XOO 300 '900^'^S^ 60C 



TeinPEiRt^TUfiC 

Fig. 3. — Tensile properties at elevated temperatures of 3^ per cent nickel steel containing 

0.27 P^^ ceM< carbon 
82 



zoo 




Pig. 4. — Tensile properties at elevated temperatures of nickeVchromium steel o the type 

J per cent nickel, I per cent chromium, and 0.4 per cent carbon 

200 , , , , ^ ^ , , , /CO 




100 zoo 300 ^00 ^500 soa 700 soo 3oa looa lltjo 

FlG. 5. — Tensile properties at elevated temperatures of chromium-vanadium, steel of the 

type I per cent chromium, 0.2 per cent vanadium, and 0.37 per cent carbon 

62954°— 21 2 83 



84 



Technologic Papers of the Bureau of Standards ivoi. in 



TABLE 4.— Tensile Properties at Elevated Temperatures of d38 Per Cent Carbon 

Steel 

[Chemical composition (per cent): C, 0.38; Mn, 0.55; P, 0.014; S, 0.013; Si, 0.14] 



Number 


Temperature of 
test 


Propor- 
tional 
limit 


Tensile 
strength 


Breaking 
strengtho 


Elonga- 
tion in 
2 inches 


Reduc- 
tion oi 
area 


A-1 


)m 


Lbs./in.2 
/ 34 900 
\ 30 500 


Lbs./in.« 
85 200 
83 200 


Lbs./in.2 


Per cent 
27.5 
33.5 


Per cent 
52.3 


A-2 




53 3 




21°C(70°F) 

92° C ... 








32 700 


84 200 




30.5 


52.8 








A-6 


34 000 
33 700 


79 400 
79 500 




28.0 
29.5 


47.6 


A-9 


92''C 




52.2 




92''Cd98''F) 

155° C 








33 850 


79 450 




28.8 


49.9 








A-10 


33 250 
32 750 


85 500 
80 200 


140 000 
137 000 


24.5 
26.0 


47.2 


A-13 


1S5°C 


48.3 




155° C (311° F).... 
241° C 






33 000 


82 850 


138 500 


25.2 


47.8 






A-12 


27 500 


87 500 
90 400 

88 900 


129 000 
127 400 
129 700 


19.0 
18.0 
17.5 


37.0 


A-17 


241° C 


32.7 


A-18 


241°C 


30 000 


36.9 




241° C (465° F).... 
292° C 




Average 


28 750 


88 950 


128 700 


18.2 


35.5 






A-8 


26 000 
24 500 
20 000 


91 500 

93 500 

94 000 




24.0 
20.0 


28.6 


A-11 


294°C 


116 700 


27.5 


A-19 


294° C 






293° C (559° F).... 
407° C 








Average 


23 500 


93 000 




22.0 


28 








A-7 


18 500 
18 500 


68 000 
72 500 


137 700 
145 800 


36.5 
34.0 


76.2 


A-15 


407° C 


73.8 




407° C (765° F).... 
463° C ... 




Average 


18 500 


70 250 


141 750 


35.2 


75.0 






A-3 


21 400 
15 300 


57 300 
56 000 




35.5 
37.0 


78 1 


A-16 


463°C 


123 700 


79.2 




463° C (855° F).... 
550°C 




Average 


18 350 


56 650 




36.2 


78.6 








A-21 


9 500 
6 000 


41 700 
38 150 


133 200 
100 300 


38.0 
43.0 


93.0 


A-22 


550° C 


92 5 




550° C (1022° F)... 




Average 


7 750 


39 950 


116 750 


40.5 


92.7 







<• Breaking strength is taken as the load observed at fracture (in pounds) divided by the reduced area 
Gn square inches). 
* Room temperature. 



French] Alloy Stecls at High Temperatures 85 

TABLE 5.— Tensile Properties at Elevated Temperatures of ^ Per Cent Nickel Steel 

Containing 0.37 Per Cent Carbon 

[Chemical composition (per cent): C, 0.37; Mn, 0.67; P, 0.021; S, 0.010; Si, 0.20; Ni, 3.43] 



Number 


Temperature of 
test 


Propor- 
tional 

limit 


Tensile 
strength 


Breaking 
strength" 


Elonga- 
tion in 
2 inches 


Reduc- 
tion oi 
area 


B-16 


(») 


Lbs./in.2 
47 000 
55 000 


Lbs./in.2 
105 150 
104 900 
103 600 
103 400 


Lbs./in.« 

172 500 
164 000 
152 000 
170 800 


Per cent 
30.5 
27.5 
27.5 
28.0 


Per cent 

50 6 


B-17 


46.7 








1 

21° C (70' F) 

92" C 




B-4 


52 500 


49.7 






Average 


51 850 


104 250 


164 800 


28.4 


46 7 






B-21 


53 000 
58 000 


97 600 
97 800 
99 600 
99 300 


169 200 

170 300 
169 500 
172 300 


28.5 
29.0 
26.0 
28.0 


54 1 


B-22 


92° C 


52.3 


B-1 


92° C 


51.3 


B-3 


92° C 




52.4 




92°C(198°F) 

155° C 






Average 


55 500 


98 600 


170 300 


27.9 


52.5 






B-6 


52 500 
56 000 
55 000 


97 100 
96 200 

98 300 
95 000 


170 800 
159 700 
169 300 
161 300 


22.0 
24.5 
25.0 
23.5 


43.2 


B-12 


1S5°C 


47.3 


B-19 


155°C 


49.4 


B-5 


155° C 


48.5 




155° C (311° F).... 

24rc 






Average 


54 500 


96 650 


165 300 


23.8 


47.1 






B-18 


42 500 


104 600 
106 200 
103 500 


181 200 
163 600 
154 300 


25.0 
22.0 
21.5 


51.5 


B-7 


241°C 


40.6 


B-8 


241°C 


42 500 


40.9 




241° C (466° F).... 
294° C 




Average 


42 500 


104 750 


166 350 


22.8 


44.3 






B-lo 


34 000 
36 500 


109 500 
108 900 


194 400 
194 800 


31.0 
32.0 


60.2 


B-9 


294° C 


59.7 




294° C (561° F).... 
407° C . . 




Average 


35 250 


109 200 


194 600 


31.5 


60.0 






B-15 


21 500 
24 000 


83 000 
83 250 


152 600 
169 700 


31.5 
31.5 


74.4 


B-13 


407° C 


74.5 




407° C (765° F).... 
463° C 






22 750 


83 150 


161 150 


31.5 


74.5 






B-14 


16 000 
18 500 


63 900 
63 500 


126 400 

127 900 


35.0 
35.0 


79.5 


B-11 


463° C 


79.7 




463° C (865° F).... 
550° C 




Average 


17 250 


63 700 


127 150 


35.0 


79.7 






B-24 


7 500 
9 000 


37 400 
33 300 


79 000 
76 300 


42.5 
44.5 


88.3 


B-25 


550° C 


89.5 




550° C (1022° F).... 






8 250 


35 350 


77 650 


43.5 


88.9 







o Breaking strengtli is taken as the load observed at fracture (in pounds) divided by tlie reduced area 
(in square inches). 
6 Room temperature. 



86 



Technologic Papers of the Bureau of Standards \voi. i6 



TABLE 6. — Tensile Properties at Elevated Temperatures of Nickel-Chromium Steel 
of the Type 3 Per Cent Nickel, 1 Per Cent Chromium, 0.4 Per Cent Carbon 

[Chemical composition (per cent): C, 0.39; Mn, 0.59; P, 0.019; S, 0.009; Si, 0.23; Ni, 3.05; Cr, 0.93] 



number 


Temperature of 
test 


Propor- 
tional 
limit 


Tensile 
strength 


Breaking 
strengtha 


Elonga- 
tion in 
2 inches 


Reduc- 
tion ol 
area 


C-14 


}W 


Lbs./in.2 
/ 58 500 
\ 58 500 


Lb8./in.2 
175 000 
171 800 


Lbs./in.2 
213 700 
207 000 


Per cen t 
10.0 
11.0 


Per cent 

22.9 


C-15 


25.2 




i 

21°C(70''F) 

92°C 


Average 


58 500 


173 400 


210 350 


10.5 


24.0 






C-2 


84 700 
74 000 


175 000 
170 000 




11.0 
11.0 


20.3 


C-3 


92° C 




23.1 




92°C(198°F) 

155° C 

155° C 






Average - 


79 350 


172 500 




11.0 


21.7 








C-6 


75 000 
72 500 


175 200 
166 000 




12.5 
12.5 


23.2 


C-7 




26.2 




155° C (311° F).... 
241° C 








73 750 


170 600 




12.5 


24.7 








C-4 


63 500 
62 500 


181 300 
178 000 




18.0 


39.6 


C-5 


241° C 








241° C (466° F) .... 

294°C 

294° C 








Average 


63 000 


179 650 
















C-8 


75 000 
80 000 


174 000 
171 000 




23.5 
23.5 


62.4 


C-9 




63.8 




294° C (561° F).... 
407° C 








77 500 


172 500 




23.5 


63.1 








C-10 


43 000 
49 000 


127 600 
132 200 


181 200 
209 000 


20.0 
20.0 


66.5 


c-u 


40'° C 


65.4 




407° C (765° F).... 
463° C 




Average 


46 000 


129 900 


195 100 


20.0 


66.0 






C-12 


22 000 
21 500 


105 000 
102 500 


137 700 
150 300 


19.0 
19.0 


59.9 


C-13 


463° C 


62.0 




463° C (865° F).... 
550° C 






21 750 


103 750 


144 000 


19.0 


61.0 






C-16 


12 000 
15 000 


72 100 
69 500 


90 000 
95 750 


19.0 
22.5 


59.0 


C-17 


550° C 


67.3 




550° C (1022° F)... 






13 500 


70 800 


92 850 


20.8 


63.2 







o Breaking strength is taken as the load observed at fracture (in t>ounds) divided by the reduced area 
(in square inches). 
i Room temperature. 



French] 



Alloy Steels at High Temperatures 



87 



TABLE 7. — Tensile Properties at Elevated Temperatures of Chromium-Vanadium 
Steel of the Type 1 Per Cent Chromium, 0.2 Per Cent Vanadium, 0.37 Per Cent 
Carbon 

[Chemical composition (per cent): C, 0.37; Mn, 0.74; P, 0.020; S, 0.023; Si, 0.21; Cr, 1.04; V, 0.17] 



Number 


Temperature of 
test 


Propor- 
tional 
limit 


Tensile 
strength 


Breaking 
strength a 


Elonga- 
tion in 
2 inches 


Reduc- 
tion of 
area 


Dl 




Lbs./in.2 
/ 88 000 
\ 88 000 


Lbs./in.2 

141 600 
147 000 


•Lbs./in.3 

236 000 
224 500 


Per cent 

20.0 
19.0 


Per cent 

55.5 


D-16 


((") 

21''C(70''F) 

92° C 


49.4 








88 000 


144 300 


230 250 


19.5 


42.5 






D-3 


81 000 
70 000 
73 000 


150 800 
135 100 
139 500 


229 400 
224 300 
224 100 


17.5 
18.0 

17.5 


48.4 


I>_4 


92° C 


51.7 


D-IS 


92° C 


45.2 




92° C (198° F) 

155° C 






74 650 


141 800 


225 950 


17.7 


48.8 






I>_7 


76 000 
79 000 


136 200. 
146 500 


240 000 
203 000 


20.0 


55.7 


I>_8 


155° C 






155° C (311° F).... 
241° C 






Avetage 


77 500 


141 350 


221 500 












J, - 


81 000 
80 000 


133 600 
137 200 


252 300 
238 700 


21.0 
19.0 


58.6 


^"^ -...-. . 


241° C 


53.3 




241° C (466° F).... 
294° C 






80 500 


135 400 


245 500 


20.0 


56.0 






I>_9 


76 000 
73 000 


145 500 
139 000 


223 400 
261 300 


19.0 


45.8 


D 10 


294°C 






294° C (561° F).... 
407° C 








74 500 


142 250 


242 350 












D_ll 


50 000 

51 500 


108 000 
115 200 


182 300 
213 000 


25.0 
25.0 


67.7 


©_12 


407° C 


71.2 




407° C (765° F).... 
463° C 






50 750 


111 600 


197 500 


25.0 


69.5 








27 000 
29 000 


97 500 
101 000 


122 500 
147 300 


23.5 
22.5 


52.9 


D_14 


463° C 


62.4 




463° C (865° F).... 
550° C 




Average -• 


28 000 


99 250 


134 900 


23.0 


57.7 






Ji-18 


16 500 

17 500 


82 600 
84 000 


118 800 
111 000 


22.0 
19.0 


61.7 


D-19 


550° C 


54.4 




550° C (1022° F) . . . 






17 000 


83 300 


114 900 


20.5 


58.0 







o Breaking strength is taken as the load observed at fracture (in pounds) divided by the reduced area 
(in square inches). 
6 Room temperature. 

Maximum strength of the carbon, 3K per cent nickel and nickel- 
chromium steels, occurs between about 240 and 300° C (465 and 
565° F), whereas the strength of the chromium-vanadium steel 
does not exceed its room temperature value within the tem- 
perature range under consideration. However, a rapid decrease 
in this factor is observed in all steels above 300° C (565° F). 

At 550° C (1020° F) the strength of the chromium-vanadium 
steel is very much greater than that of the other alloys and more 
than twice that of the carbon steel. It has likewise decreased 
the least in strength from its room temperature value, as shown 
in Table 8. However, at all temperatures below about 475° C 
(885° F) the strength of the nickel-chromium steel is greater than 
that of the chromium-vanadium. 



88 



Technologic Papers of the Bureau of Standards ivoi. i6 



TABLE 8. — Comparison of Tensile Strengths of Carbon and Alloy Steels at Room 

Temperature and 550° C 





Tensile 
strength at 
room tem- 
perature 


At 550° C (1022° F) 


Steel 


Actual 
tensile 
strength 


Decrease 
from room 

tem- 
perature 

value 


Ratio of 

tensile 

strengths 

with carbon 

steel as 

unity 


Carbon 


Lbs./in.2 

84 200 

104 250 

173 400 

144 300 


Lbs./in.2 
39 950 
35 350 
70 800 
83 300 


Per cent 
52.5 
66.0 
59.1 
42.4 


1-0 
.9 


Nickel 


TSrirTrel-rhrnmliim 


1.8 


Chroml^im.vnpflrliitin 


2.1 







(6) ProportionaIv Limit. — ^The proportional limits of the 
carbon, 3>^ per cent nickel and nickel-chromium steels, increase 
with first rise in temperature and reach maximum values in the 
neighborhood of 150*^ C (300° F), whereas that of the chromium- 
vanadium steel is greatest at room temperattu-e and, following a 
marked decrease, again increases perceptibly between about 150 
to 250° C (300 to 480° F) before final decrease occurs. While the 
maximum value of the limit of proportionality of the nickel- 
chromium steel occurs at about 150° C (300° F) and is followed 
by a material decrease, a second rise in value is observed at 
about 300° C (570° F), so that this factor is maintained above 
its room temperattire value until temperatures above about 370° C 
(700° F) are reached. 

The limit of proportionality of the chromium-vanadium steel 
^•t 550° C (1020° F) has decreased proportionally more than either 
the carbon or nickel-chromium steels, as shown in Table 9, but 
its value at the high temperature indicated is greater than either 
of the latter and more than twice that of the carbon steel. 

TABLE 9. — Comparison of Proportional Limits of Carbon and Alloy Steels at Room 

Temperature and 550° C 





Proportional 

limit at 
room tem- 
perature 


At 550° C (1022° F) 


steel 


Actual 

proportional 

limit 


Decrease 

from room 

temperature 

value 


Ratio of 
proportional 
limits with 
carbon steel 

as unity 


Carbon 


Lbs./in.2 
32 700 
51 850 
58 500 
88 000 


Lbs./in.2 

7750 

8250 

13 500 

17 000 


Per cent 
76.3 
84.2 
77.6 
80.7 


1.0 


Nickel 


1.1 


Nirkfil-chrnmium , , , , 


1.7 


Cliromiuni-vanacIiuTTi , . 


2.2 







French] 



Alloy Steels at High Temperatures 



89 



(c) Ei<ONGATiON AND REDUCTION OP Area. — ^The effect of 
temperature is greater upon the values of reduction of area than 
elongation. In general, the inflections in the temperatiu'e elonga- 
tion and temperature reduction of area curves shown in Figs. 
2,3,4, ^iid 5 ar^ so varied that no attempt will be made to describe 
them . However, several generalizations may be made . The carbon 
and 3 % per cent nickel steels behave similarly, in that rise in tem- 
perature is accompanied by a general decrease in ductility, which 
is followed above the range 200 to 300° C (390 to 565° F) by an 
increase until at 550° C (1020° F) values of elongation and reduction 
of area are greater than those observed at room temperature. 

The elongation of the chromium-vanadium steel is about the 
same at 550° C (1020"* F) as at room temperature and does not 
show any very great changes throughout this temperature range, 
whereas elongation of the nickel-chromium steel increases to a 
maximum at about 295° C (565° F) (blue heat). 

While the carbon and nickel steels are much more ductile at 
550° C (i020° F) than either the chromium-vanadium or nickel- 
chromium steels, as shown in Tables 10 and 11, yet the last two 
alloys have high ductility, and the latter shows by far the greatest 
increase over its room temperature value. 

TABLE 10. — Comparison of Elongations of Carbon and Alloy Steels at Room Tem- 

perattire and 550° C 



Steel 



Elongation 
in 2 inches 

at room 
temperature 



At 550° C (1022° F) 



Actual 
elongation 
in 2 inches 



Increase 

from room 

temperature 

value 



Ratio of 
elongations 
with carbon 

steel as 
unity 



Carbon 

Nickel 

Nickel-chromium 

Chromium-vanadium 



Per cent 
30.5 
28.4 
10.5 
19.5 



Per cent 

40.5 
43.5 
20.8 
20.5 



Per cent 

32.8 

51.4 

98.0 

5.1 



1.0 

1.1 

.5 

.5 



TABLE 11. Comparison of Reductions of Area of Carbon and Alloy Steels at 

Room Temperature and 550° C 





Reduction 

of area 

at room 

temperature 


At 550° C (1022° F) 


steel 


Actual 

reduction 

of area 


Increase 

from room 

temperature 

value 


Ratio of 
reductions 

of area 

with carbon 

steel as 

imity 




Per cent 

52.8 
46.7 
24.0 
42.5 


Per cent 

92.7 
88.9 
63.2 
58.0 


Per cent 

75.5 

90.3 

163.3 

36.5 


1.0 


Nickel 


1.0 




.7 




.6 







90 



Technologic Papers of the Bureau of Standards Woi. 16 



(d) Breaking Strength. — ^The strength at fracture of the 
different steels tested, obtained by dividing the load observed at 
the moment of breaking by the reduced area, is shown in Fig. 6. 
While the data are incomplete and in some cases the variations 
in duplicate determinations are wide, the results are interesting 
when taken in conjunction with the changes previously described, 
for at 550° C (1020° F) the highest breaking strength is shown 



&o 




Fig. 6. — Breaking strength at elevated temperatures of carbon, nickel, nickel-chromium, 
and chromium-vanadium steels. {For compositions refer to Table j) 

by the chromium-vanadium and carbon steels and the lowest 
value is observed in the alloy containing 3X per cent nickel. 

2. MICROSCOPIC EXAMINATION OF FRACTURES 

The fracture of steels subjected to tensile stress at room tem- 
perature is transcrystalline, while at high temperatures it takes 
place at the grain boundaries. The change from transcrystalline 
to intercrystalline fractures will occur beginning at temperatures 
somewhat above that of equal cohesion of the amorphous and 
crystalline phases, but the temperatures at which these fractures 



Technologic Papers of the Bureau of Standards, Vol. 15 







— Wf""^^ 







Fig. 7. — Microplwtographs of fractures of carbon and j 1/2 per cent 
. nickel steels broken in tension at high temperatures 

(a) Specimen A 16. Broken at 463° C. X300 

(5) Specimen A 22. Brol^en at 530° C. X500 

(c) Specimen B 11, Broken at 463° C. X500 

(d) Specimen B 24. Broken at 550° C. Xiooo 

All specimens etched with s per cent picric acid in alcohol 



Teclinologic Papers of the Bureau of Standards, Vol. 16 




Fig. 8. — Micro photographs of fractures of nickel-chromium and 
chrofnium-vanadium steels broken in tension at high temperatures 

(a) Specimen C S. Broken at 294° C. Xiooo 

(b) Specimen C 13. Broken at 463° C. X500 

(c) Specimen C 16. Broken at 550° C. X500 

(d) Specimen D i;. Broken at 463° C. Xiooo 
(c) Specimen D I S. Broken at 550° C. X500 

a, d, and e etclied with 5 per cent picric acid in alcohol; b and c with 2 per cent 
nitric acid in alcohol 



French] Alloy Stcels at High Temperatures 91 

first appear in a given alloy depend upon the rate of loading.^ The 
faster the load is applied the higher is the temperature required 
to produce intercrystalHne breaks. 

Jeffries states that in most metals the equicohesive temperature 
occurs at about 0.35 to 0.45 of the melting point on the absolute 
temperature scale, so that for steels the change from fractures 
across the grains to those along the crystal boundaries should on 
slow loading first appear in the neighborhood of 550° C (1020° F). 
This temperature is approximately the highest at which tensile 
tests were made, and, as these were Hkewise considered of par- 
ticular interest from the standpoint of operation in the Haber 
process, specimens of the several steels tested were examined 
under the microscope to determine" the character of the fracttues. 

Typical microphotographs are reproduced in Figs. 7 and 8, 
and while no general statements can be made with certainty they 
show the tendency of the fracture in the carbon and 3^ per cent 
nickel steels to follow the grain boundaries when broken at about 
550° C (1020° F). 

The outstanding feature of the nickel-chromium steel is the 
fineness of the structure, making it difficult to determine the 
character of the break, while in the case of the chromium-vana- 
dium steel the fractiu-es appear more nearly intracrystalline (8e) 
even at the highest temperatures under investigation. 

V. SUMMARY 

The following points appear to deserve emphasis in connec- 
tion with the tests previously described: 

1. Of the four steels tested in normaUzed condition it appears 
that the two alloys containing chromium show greater resistance 
to weakening by increase in temperatmre to about 550° C (1020° 
F) than either the plain carbon or 3>^ per cent nickel steels, and 
at this highest temperatture the chromiiun-vanadium steel is to 
be preferred from the standpoint of high tensile strength and 
limit of proportionaUty. 

2. The carbon and 3^^ per cent nickel steels behave aHke with 
rise in temperature, and at about 550° C (1020° F) the addition 
of the nickel appears to have a very small effect on the tensile 
properties of the carbon steel. 

'Zay Jeffries, "Effect of temperature, defonnatian, and grain size on the mechanical properties of 
metals," Trans. A. I. M. E., 60, p. 474; 1919. 



92 Technologic Papers of the Bureau of Standards [Voi. i6 

3. At 550° C (1020° F) the strength and Hmit of proportionality 
of the chromium- vanadium steel are more than twice that of the 
carbon steel, while the ductility of the former, as measiured by 
elongation and reduction of area, is about half that of the latter, 
though still quite high. However, at all temperatures below about 
475° C (885° F) the strength of the nickel-chromium steel is 
greater than that of the chromium-vanadium and both show 
higher strength values throughout the range 20 to 550° C (70 to 
1020° F) than the carbon or 3^ per cent nickel steels. 

4. While no general statements regarding types of fractures 
can be made with certainty, the tendency of carbon and 3^ per 
cent nickel steels at about 550° C (1020* F) is to follow the grain 
boundaries, while at the same temperature the fractures of the 
chromium-vanadium steel appear largely transcrystalline. 

ACKNOWLEDGMENT 

In conclusion acknowledgment is made to C. B. Lermond, 
mechanical draftsman, Ordnance Department, and T. B- Hamill, 
laboratory apprentice, Bureau of Standards, for carrying out 
the greater part of the routine tensile tests reported in this paper. 

Washington, August i, 1921. 



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